1. Field of the Invention
The invention pertains to apparatus for applying labels or the like to objects and more particularly to automated machinery for applying labels or the like to objects of different dimensions on a continuously moving conveyor.
2. Prior Art
Automated machinery is known which applies imprinted labels to packages moving along a conveyor belt. Typically, labels are supplied on an elongated backing strip which may be retained on a reel. The labels are removed from the backing strip by the applicator machinery and retained against a grid by means of vacuum. When a package is aligned with the head, an air blast transfers the label from the grid to the package to be labeled. One such prior art arrangement is shown, for example, in U.S. Pat. No. 3,885,705, issued May 27, 1975.
Using an air blast to apply a label to a package requires that the applicator be in relatively close proximity to a surface of the package, typically the top surface. When packages of, for example, different heights are to be labeled, it is necessary to adjust the relative distance between the applicator and the top surface of the package for the various packages. Preferably, this will be done automatically as packages of different heights are moved past an applicator machine on a conveyor. In one prior art arrangement, disclosed in U.S. Pat. No. 3,729,362, issued Apr. 24, 1973, an applicator pad has a cluster of vertically extending fingers which engage a label deposited on the pad and transfer the label to an object in alignment with the applicator pad. One clear disadvantage of such an arrangement is that only a limited height difference between products can be accommodated. Furthermore, such an arrangement is inherently relatively slow since the fingers must be retracted before the next label can be deposited onto the applicator pad for application to a subsequently arriving product.
It is a general problem of the prior art to produce label application machinery that can handle products of greatly varying dimensions on a relatively rapidly moving conveyor with a limited distance between products. Preferably, the time between application of labels on successively appearing products of different heights will be less than 500 milliseconds. Such an arrangement requires very rapidly adjustable applicators. It has long been proposed to move an applicator head on a stationary support structure, by means of a linear stepper motor in which a moving element is moved along a longitudinally extending platen. A drawback of such devices is that they are particularly adapted for high-speed, low-mass applications, while the mass of the label applicator head is substantial.
When labels are applied to products by a blast of air, it is common to provide a secondary impression roller to press the label against the product and provide a secondary wipe-down effect on the label. Prior art label applying apparatus which makes adjustments for varying heights of products to be labeled do not provide such a secondary impression roller, thereby providing a less reliable adhesion of the labels.
It is well known that occasionally a label applying machine, for one reason or another, does not deposit a label on the product for which it was intended. Since such labels are generally individually printed for the products as they are conveyed to the applicator machine, an unused label must be removed to avoid mislabeling a subsequently arriving product. To this end, a device known as a pick plate is temporarily aligned with the applicator and the standard air blast is used to deposit the label onto the pick plate. Typically, such a pick plate extends below the applicator head and occasionally snags a product. In a system using a height adjustable applicator, severe damage to the product may result as well as damage to the equipment.